MPLS route is still active in routing table even its corresponding OSPF route is not listed

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Hi There,


I found MPLS route is still active in routing table even its corresponding OSPF route is not listed in routing table.


Ori  Destination        Gateway         Mtr  Flags         VLAN       Duration
 mp  192.17.80.55/32    172.17.79.1     1    U--D---um-L-- CR1-DR1_902 0d:2h:57m:41s
 mp  192.17.80.55/32    172.17.79.85    1    U--D---um-L-- CR1-DR1_782 0d:3h:37m:45s
#or  192.17.80.55/32    172.17.79.85    12   UG-D---um--f- CR1-DR1_782 0d:3h:37m:46s

Even increasing the OSPF cost of the link, its mpls route is still active in routing table and traffic is going via that link.

How can I increase the metric of mpls route ?

Best Regards,
Ronie


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Ronie Singh

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Posted 2 weeks ago

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Stephen Williams, Employee

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The problem is with your route priority being that they are both the same subnet mask.  You can change the route priority with the "configure iproute priority" command.


Switch# show iproute priority
Direct                 10      
MPLS                   20      
Blackhole              50      
Static                 1100    
ICMP                   1200    
EBGP                   1700    
IBGP                   1900    
OSPFIntra              2200    
OSPFInter              2300    
Isis                   2350    
IsisL1                 2360    
IsisL2                 2370    
RIP                    2400    
OSPFAsExt              3100    
OSPFExt1               3200    
OSPFExt2               3300    
IsisL1Ext              3400    
IsisL2Ext              3500    
Bootp                  5000    

(Edited)
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Grosjean, Stephane, Employee

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I don't understand the question. In your output, only the OSPF route is selected and installed in the FIB.
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Ronie Singh

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Let me elaborate. Even only the single OSPF route is there, the path is chosen based on the mpls routes. There are two mpls routes as you can see in the output shared above, the first mpls route is taken as primary active path (its corresponding OSPF route is not even shown in routing table).

Is that due to the reason the  cmd "enable ospf mpls-next-hop" is applied on the node ? Your further explanation on this would be highly appreciated.


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Grosjean, Stephane, Employee

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Oh, then yes, I think so, you are telling the OS to use the MPLS LSP with that command. Check the User Guide (p.1222 in the 22.6 version) for "OSPF Calculated LSP Next Hops" for more details.

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Ronie Singh

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The question being is why following mpls route is shown in routing table in the first place ?

mp  192.17.80.55/32    172.17.79.1     1    U--D---um-L-- CR1-DR1_902 0d:2h:57m:41s

Since there is only one ospf route (best route) is selected, there should be only one mpls route with the same next-hop (as in ospf route).

Your further explanation on this would be highly appreciated. 

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Grosjean, Stephane, Employee

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I double-checked with a real expert.

There are no OSPF Calculated routes here.  If there were, there would be a lower case “L” instead of the uppercase one.  MPLS next-hops may even not be turned on (since neither MPLS route is selected for routing, but do have a lower cost than the OSPF route). Can you confirm that?

The MPLS routes are ECMP here.  This could be because OSPF reports both as equal cost, which I guess isn’t the case, since OSPF only shows one route, or it could also be due to adjacent nodes.  Is CR1-DR1_902 connect directly to 192.17.80.55 from this node? 

Can you share the output of "show mpls ldp peer detail"?






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Erik Auerswald, Embassador

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Hi,

I would expect the flags Lf for an active IP over MPLS route (using enable iproute mpls-next-hop) as in the following example:
#mp  10.0.0.2/32        10.1.0.2        1    U--D---um-Lf- t-s2-s3    0d:0h:1m:22s
 oa  10.0.0.2/32        10.1.0.2        14   UG-D---um---- t-s2-s3    0d:0h:14m:58s

It seems to me as if only the OSPF route is used for IP forwarding in the question above.

Thus the problem seems to be more that there are two LSPs available and possibly advertised via LDP, while only one LSP corresponding to the least cost path is expected.

This leaves the question of why there is the other LSP corresponding to a non-least cost path.

Thanks,
Erik
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Ronie Singh

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Yes, mpls-next-hop is turned on as follow.

DR1.6 # show configuration | inc next-hop
enable ospf mpls-next-hop
DR1.7 #

And also CR1-DR1_901 is directly connected to 192.17.80.55 but its ospf cost is set to 40 where the primary link CR1-DR1_782 is set to 2.

DR1.7# show ospf interfaces

 VLAN      IP Address         AREA ID         Flags      Cost State   Neighbors
   
CR1-DR1     172.17.79.86   /30 100.0.0.0       -rif---       2/C P2P       1      
CR1-DR1     172.17.79.5    /29 100.0.0.0       -rif---      40/C P2P       1  

DR1.9 # show ospf neighbor | inc 192.17.80.55
192.17.80.55      1 FULL      /DROTHER 00:08:09:59/00:00:00:09  172.17.79.85    CR1-DR1
192.17.80.55      0 FULL      /DROTHER 00:00:07:09/00:00:00:03  172.17.79.1      CR1-DR1    

This must be a bug and Extreme really need to fix this.
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Grosjean, Stephane, Employee

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Hi,

I'm not GTAC, so if you think there's a bug that needs to be fixed, you should open a case.
Can you please share the output of "show mpls ldp peer detail"?
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Ronie Singh

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OK. If you say so. I used to contact GTAC but now, I am really fed up with their support. They kept asking to provide output of cmd again and again. I better save time by looking workaround solution.

Due to the privacy, I can't share the output you are asking for. Thank you for your help till here.

Best regards,
Ronie
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Grosjean, Stephane, Employee

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You need to look at that output to check if there's no LDP LSP between the adjacent nodes. You may have one created, explaining your behavior.